This invention relates to a plate filter having a plurality of shiftable filter elements comprising filter plates and frames arranged in an alternating sequence on a filter stand. The plate filter includes a filter element closing device which presses the filter elements together to form a compressed filter plate stack. At two opposite edges of some of the filter elements deflecting rolls are provided which support an endless filter cloth passing in a zigzag fashion between subsequent filter elements. At least some of the deflecting rolls are driven rolls. The plate filter further has a filter cloth driving mechanism which moves the filter cloth through the filter plate stack in the open (separated) state of the latter. At least some of the deflecting rolls (filter cloth support rolls) are, at one side of the filter plate stack, at least at one roll end, provided with a sprocket affixed thereto which meshes with a flexible, form-locking and endless driving means interconnecting several sprockets and being driven by a drive motor.
A plate filter of the above-outlined type including vertically oriented filter plates is disclosed in German Auslegeschrift (application published after examination) No. 2,012,400. It is a disadvantage of the known structure that upon closing the filter plate stack, the driving chain or driving belt length which is normally meshing with the sprockets from below, drops loose therefrom and hangs in a slack manner. In addition, for driving the filter cloth supporting (deflecting) rolls, two intersecting chains have to be positioned side-by-side so that in the closed state of the plate filter, side-by-side arranged, offset, slack chain lengths are present. The respective underlying return flight of the two chains is supported on end rollers on the stationary end plate as well as on the displaceable head plate of the plate filter so that upon closing of the plate filter the two return flights also hang loosely along their entire length.
During the closed state of the filter plate stack, almost during the entire opening process and almost during the entire closing process, neither the respective driving flight nor the respective return flight of the driving chains are guided; rather, there are formed side-by-side situated, freely suspended chain loops. Since particularly after a longer service period the roller chains or side bar chains may also move in a direction transversely to the pivotal plane of the chain links, small jars which cannot be safely avoided during the displacements, are sufficient to cause entanglement of the two loosely hanging chain flights. Such an occurrence may lead to operational disturbances and damages. It is a further disadvantage of the above-outlined known construction that it can be used only in plate filters having vertically oriented filter plates.
U.S. Pat. No. 4,289,622 discloses a filter cloth transporting mechanism in which the roller chain serving as the drive means is guided in such a manner by means of a combination of a sprocket and a deflecting roller in each filter element that the roller chain remains connected--independently from the open or closed state of the filter plate stack--the sprockets and the deflecting rolls even during the opening and closing motion of the filter elements. It is, however, a disadvantage of this structure that the entire driving output for the filter cloth transport has to be channelled through one roller chain, or more often, through two roller chains so that the roller chains have to be of sturdy construction. Further, this arrangement cannot be used in multiple drives for large filter units.